Group 9 element

Group 9 in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson group 8 ←    → group 10
IUPAC group number 9 Name by element cobalt group CAS group number (US, pattern A-B-A) part of VIIIB old IUPAC number (Europe, pattern A-B) part of VIII
↓ Period
4	Cobalt (Co) 27 Transition metal
5	Rhodium (Rh) 45 Transition metal
6	Iridium (Ir) 77 Transition metal
7	Meitnerium (Mt) 109 unknown chemical properties
Legend primordial element synthetic element Atomic number color: black=solid

Group 9 is a group (column) of chemical elements in the periodic table. Members are cobalt (Co), rhodium (Rh), iridium (Ir) and meitnerium (Mt). These are all transition metals in the d-block.

Like other groups, the members of this family show patterns in electron configuration, especially in the outermost shells, resulting in trends in chemical behavior; however, rhodium deviates from the pattern.

"Group 9" is the modern standard designation for this group, adopted by the IUPAC in 1990.

In the older group naming systems, this group was combined with group 8 (iron, ruthenium, osmium, and hassium) and group 10 (nickel, palladium, platinum, and darmstadtium) and called group "VIIIB" in the Chemical Abstracts Service (CAS) "U.S. system", or "VIII" in the old IUPAC (pre-1990) "European system" (and in Mendeleev's original table).

Chemistry

Z	Element	No. of electrons per shell	M.P.	B.P.	Year of Discovery	Discoverer
27	cobalt	2, 8, 15, 2	1768 K 1495 °C	3200 K 2927 °C	~1735	Georg Brandt
45	rhodium	2, 8, 18, 16, 1	2237 K 1964 °C	3968 K 3695 °C	1803	W. H. Wollaston
77	iridium	2, 8, 18, 32, 15, 2	2719 K 2446 °C	4403 K 4130 °C	1803	S. Tennant
109	meitnerium	2, 8, 18, 32, 32, 15, 2[*]	—	—	1982	P. Armbruster and G. Münzenberg

[*] Predicted.

The first three elements are hard silvery-white metals:

Cobalt is a metallic element that can be used to turn glass a deep blue color.

Rhodium can be used in jewelry as a shiny metal.

Iridium is mainly used as a hardening agent for platinum alloys.

All known isotopes of meitnerium are radioactive with short half-lives. Only minute quantities have been synthesized in laboratories. It has not been isolated in pure form, and its physical and chemical properties have not been determined yet.

See also

• Iron group
• Platinum group